After a spell in Moscow working for Comintern he left the Communist Party to join the more moderate Socialist Republican Union, which counted Marcel Déat amongst its membership, in 1929.

[6] Marion was part of a loose group of leading members, unofficially led by Pierre Pucheu, who left the party together in early 1939.

His power grew as he was elected to the controlling committee of the Legion of French Volunteers Against Bolshevism and, along with Jacques Benoist-Méchin, pushed to Pierre Laval the idea that the group should become an official arm of the Vichy government.

[11] Marion returned to office soon afterwards following Henriot's death and served in his former position when the Vichy government was shifted to Belfort, although by then it was effectively powerless.

Although he took no further role in politics Marion was reported as advising friends and supporters to vote for the Rally of the French People in the immediate post-war elections.